It is known that reproducing images on a photosensitive medium, a negative photographic paper for instance, consists of placing said paper in a lightproof room, and then exposing it with light carrying information relative to the image to be reproduced.
Said light can be produced, for instance, by a lamp of a suitable power and colour temperature; it is conveyed by an optical device, through a film carrying a negative print of the image to be reproduced and then to the photosensitive surface of the photographic paper.
According to further reproduction modes, equally known to a skilled technician, the photosensitive medium can consist of autopositive photographic paper, either self-developing or not. It can be exposed by a light source that lights a film carrying the positive image, or by the light directly coming from a subject to be photographed, by means of a suitable photographic camera.
At this point, the image is in a hidden state, and it is subsequently developed and made stable by submitting the photographic paper to suitable chemical processes.
Said processes usually comprise the steps of immersing the photographic paper into a first developing bath, for a first pre-defined period of time, during which the image is developed; the paper sheet is then immersed into a second bath, containing a fixing or bleaching liquid, for a second pre-defined period of time. One or more immersions into a water bath follow, in order to remove the fixing traces. The photographic paper is then dried.
The above described developing process is carried out automatically by known apparatuses, often with some variants and improvements.
Said apparatuses consist of a series of consecutively placed tanks, each containing a suitable processing liquid, at a given temperature, and of dragging members, fit to convey a photosensitive medium into said tanks according to a pre-defined timing. A continuous web made of the above medium, previously exposed with photographic images, is then inserted into the developing tank first, then into the fixing or bleaching tank, and finally into the washing tank. The web is subsequently dried and cut, in order to separate each photogram.
Apparatuses like the one described above require, in order to operate correctly, that each tank is loaded with large quantities of the respective developing product. Said products must be replaced after a given number of operating cycles, since their efficiency tends to decrease; otherwise, small quantities of new product have to be periodically added to the exhausting product. Thus, it is very difficult to keep the physical parameters of the developing products constant, which is necessary to have a constant output quality. Moreover, it is difficult to maintain a constant temperature inside the tanks, which is also very important to achieve good quality printing results. Finally, power consumption is normally high, because big quantities of developing products must be thermoregulated.
A further apparatus for developing a single sheet of photosensitive medium is also disclosed in the Italian patent Application N. B094A 000481, in the name of the same Applicant. Said apparatus is of the so-called micro-tank or laminar tank type, and solves most of the aforesaid problems by using a developing tank having a very small internal volume, which is contained inside a thermoregulating device.
Said developing tank is fit to receive a sheet of photosensitive medium to be processed inside a laminar hollow. It is fed in sequence with developing products, fixing products and washing products, generally in a liquid state, by means of suitable, separate loading means. Each product stays into the tank just for the time required to operate optimally, after that it is flown out of the tank by means of draining means. This latter is for instance made of a solenoid valve, connected to a conduit, which conveys said products toward one or more draining or recycling containers.
The photosensitive sheet is thus processed in a sequential way, by a developing cycle, eventually followed by one or more washing cycles, and then by a fixing cycle, which is in turn followed by one or more tank washing cycles.
The aforesaid device carries out the sheet processing operations in an economic, functional and completely automatic way but, since it works with a single tank, it can suffer for some problems relating a contamination of the developing product by the fixing product. This can especially happen because of undesired leakage of fixing product occurring on the means for loading said product. Said leakage is generally due to some residual dripping from the output nozzle of said loading means. Normally it is limited to one or two drips of fixing product but, if this happens during a developing cycle, the features of the developing product can be substantially modified.
Moreover the operation of said device is usually not very fast, since it carries out the developing and fixing cycles in a sequential way, furthermore interposing one or more tank washing cycles in between.
A further micro-tank apparatus, disclosed in the Italian patent application N. B095A 000399, in the name of the same Applicant, is provided with a pair of small-sized tanks, of the above described type, which are cascade-operating. One of those carries out the developing cycle, and the remaining one carries out the fixing and washing cycles for a sheet of photosensitive medium. This guarantees a better safety against the developing product contamination, and speeds up the processing operations when several photosensitive sheets have to be processed. Indeed, with the above described apparatus, a subsequent photosensitive sheet can be developed when a previous sheet is subject to the fixing treatment.
The above described processing apparatuses don't attain completely satisfactory operating results when the developing and fixing times are comparable with the time required for inserting and taking out the photosensitive sheet into and from the tank. In fact, because of the time required for inserting or for taking out the sheet, the lower portion of this latter stays into contact with the developing products for a longer time than its upper portion. Since the market now offers developing products which allow a substantial reduction of the photosensitive medium processing times, thus speeding up the whole processing operations, said difference can lead to some visible effects on the processed photosensitive sheet.